Device for making seams on three-dimensional objects

ABSTRACT

For making seams on three-dimensional objects, a manipulator (20) is used at the manipulator arm (19) of which a sewing machine (18) is secured. The cuttings (12,14) to be sewn are fixed to a holding device (10), and the sewing machine (18) sews the protruding edge strips (16) which confront each other. The sewing machine (18) can be guided by the manipulator arm (19) along the intended seam line at constant speed. While the needle penetrates the material, the sewing machine being guided on a guide (21) by means of a carriage (22) is driven in a direction opposite to the feeding direction of the manipulator so that the sewing machine is at a temporary standstill with respect to the holding device (10). After completion of the stitch, the carriage (22) is advanced on the guide (21) in feeding direction so that the sewing machine catches up with the lag. With each stitch, the edge strip (16) is clamped between a needle plate and a presser of the sewing machine.

BACKGROUND OF THE INVENTION

The invention relates to a device for making seams on three-dimensionalobjects made of materials such as textile woven materials, leather,synthetics or similar materials. Such devices are used for theproduction of clothing, upholstery for seating furniture andautomobiles, and for the production of shoes.

Usually, three-dimensional objects such as envelopes made of fabric aremanufactured in such a way that pre-made two-dimensional cuttings aresewn lying flat on top of each other with a sewing machine. The twocuttings are sewn together at an exactly specified distance from thecutting edges. Beforehand, the cuttings have been provided with markingswhich have to match during sewing, and it is also necessary to displacethe cuttings relative to each other during sewing. Joining of thecuttings by means of a sewing machine is very time-consuming andrequires a high degree of routine of the operator who has to guide thecuttings and operate the sewing machine. Because of the relatively slowmanual control, the performance possibilities of the sewing machine arenot fully utilized. The feeding of the materials is made by the sewingmachine intermittently between the penetration movements of the needle.From DE 33 38 405 A1, a device for producing three-dimensional articlesprovided with seams is known wherein a sewing machine is attached to amanipulator in the form of a robot arm. This sewing machine is moved bythe manipulator in such a manner that said sewing machine is guidedalong the intended seam line of the two cuttings to be sewn. Anunder-thread bobbin grips underneath the cuttings to be sewn and apresser presses against the top cutting. The lower cutting is supportedby a brush bed through which the under-thread bobbin moves.

A similar sewing device is known from EP 0 344 400 A1. Here, too, asewing machine is secured to the manipulator arm of a robot, the detailsof which sewing machine, however, are not described.

The known devices on which a sewing machine is moved by a manipulator ina three-dimensional system involve the difficulty of obtaining a neatand distortion-free seam and still carrying out the sewing action athigh working speed.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a vice for making seams onthree-dimensional objects, which permits the production of perfect anddistortion-free seams.

This object is solved, according to the invention; with the featuresindicated in claim 1.

In the sewing device according to the invention, the sewing machinecomprises a sewing head the movement of which is controlled such thatduring the penetrations of the needle into the material, it is at astandstill relative to the holding device carrying the workpiece. Thesestandstill actions can be produced in different ways. One possibility isto move the manipulator arm in coordination with the needle movements ofthe sewing machine along the seam line such that said manipulator arm isat a standstill during the penetration and withdrawal movements of theneedle and only moves the sewing machine when the needle is pulled outof the material. Another possibility envisages that the sewing head ismovably guided in a linear direction on the manipulator arm such that atthe point when the needle is in the material, said sewing head is movedbackward along the intended seam line relative to the manipulator arm atabout the same speed and afterwards, when the needle is pulled out ofthe material, the amount of lost movement is caught up again. Themanipulator arm can then be moved at constant speed such that the toolcenter point of the manipulator moves at constant speed along the seamline, the sewing machine, however, alternately falling short of the toolcenter point and catching up the lost movement again. To this end, aguide is secured to the manipulator arm which guide is always alignedparallel to the intended seam line and along which the entire sewingmachine is linearly guided. Finally, it is also possible to move theholding device for the fabric by means of the manipulator arm while thesewing machine is stationary, the entire sewing machine or only theparts of its sewing head being linearly moved to carry out the followermovement.

It is also within the scope of the invention to mount the sewing machinefirmly on the manipulator arm and move the sewing head or the individualcomponents thereof along linear ways of displacement such that thesewing head is at a standstill relative to the workpiece duringstitching movements of the needle. In this case, too, the manipulatorarm can be moved at constant speed, while the back and forthcompensating movements are carried out exclusively by the sewing headrelative to the sewing machine.

Continuous movement of the manipulator arm has the advantage that themasses which have to be moved intermittently dependent on the stitchmovements of the needle can be kept relatively small and that it is notnecessary to mutually coordinate the movements of the manipulator armand the stitching movements of the needle.

In the sewing machine according to the invention, the feeding stroke forsewing the seam is made exclusively by the manipulator arm while theworkpiece itself is at a standstill. Here, the holding device carryingthe workpiece does not necessarily have to be absolutely fixed, but canbe fitted so that it can be turned, for example. It is important thatthe sewing machine itself has no feeding device and that the material isnot moved further between two stitches.

For the purpose of permitting a relative movement of the sewing headwith respect to the workpiece between two stitches, the needle plate andthe presser are moved apart when the needle is pulled out of thematerial. In this state, the sewing head (or the entire sewing machine)can be moved by one stitch length relative to the workpiece. After that,the material is again clamped between needle plate and presser in orderto provide for an exact position of the workpiece for the next needlestitch and an exact mutual alignment of the cuttings to be sewn.

Hereinafter, embodiments of the invention are explained in detail withreference to the drawings.

In the figures:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a holding device with cuttings to be sewn together securedon it,

FIG. 2 an illustration of the holding device together with themanipulator and the sewing machine mounted therein,

FIG. 3 a section along line III--III of FIG. 2,

FIG. 4 a front view of the sewing machine,

FIG. 5 a diagram of the time coordination of the movements of the sewinghead with the stitch movements of the needle, and

FIG. 6 a side view of another embodiment in which the sewing head islinearly movable relative to the sewing machine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a holding device 10 carrying individual cuttings which areconfronted with each other in order to form a three-dimensional hollowobject from two-dimensional material. The workpiece to be manufacturedthe cuttings of which are secured on the holding device 10 consists ofthe sleeve for an armrest of a motor vehicle.

The holding device 10 comprises a basic body 11 about which a cutting 12in the form of a bandshaped strip is placed. This cutting 12 is securedon the basic body 11 by holding plates 13 which are pressed against thecutting from the outside. The cutting 12 encompasses the basic body 11.The side of the ring formed by the cutting 12 is to be closed by acutting 14 in the form of a side part to be sewn on. The cutting 14 isplaced against the side surface of the basic body 11 and held there by aholding plate 15 which is pressed against the basic body. Holding of theholding plates 13 and 15 on the basic body 11 can be effected, forexample, by magnets or by suction.

The cuttings 12 and 14 are of such a size that they overlap at thecircumferential edges where they form edge strips 16 (see also FIG. 3).At the root of these edge strips 16, the seam 17 is produced.

FIG. 2 shows the holding device 10 which is fitted on a holder (notshown) in a stationary manner, and a sewing machine 18 mounted on amanipulator arm 19. The manipulator arm 19 is a part of the manipulator20 which, in this case, is an industrial robot with a plurality ofmovement axes, for example with six or eight movement axes. Themanipulator 20 is numerically controlled such that the tool centerpoint, i.e. the effective point of a tool firmly fitted on themanipulator arm 19, can be moved along a predetermined movement path.Programming of the manipulator 20 can be made such that the manipulatorarm 19 with the tool secured thereto is manually guided along theintended processing line in a teaching phase. The path values recordedin this way are stored, and subsequently, the manipulator 20 iscontrolled such that the manipulator arm 19 performs the same movementsin a controlled manner which were carried out in the teaching phase. Thetool secured on the manipulator arm consists of the sewing machine 18 inthis case.

On the manipulator arm 19, a linear guide 21 is secured along which acarriage 22 which carries the sewing machine 18 can be moved. The guide21 is aligned transversely to the needle of the sewing machine 18 and itextends parallel to the seam line 17 to be produced. The carriage 22 isdriven by a drive (not illustrated). This drive may consist of the drivemotor 23 of the sewing machine, in which case the carriage movement maybe produced by a cam disk moved by this drive motor 23.

According to FIG. 3, the drive motor 23 of the sewing machine 18 drivesa drive shaft 25 via a belt drive 24, said drive shaft driving thecomponents of the sewing machine in the known manner. The sewing machinecomprises a sewing head 26 which is arranged in a fixed association withrespect to the sewing machine housing 18a. Belonging to the sewing head26 are the needle lever 27 which is fitted to a back and forth movingturned shaft 28 and carries the curved needle 29, a needle plate 30which forms an abutment for the double-layered edge strip 16 andcomprises a cutout for penetration of the needle 29, a presser 31arranged opposite the needle plate 30 and a shuttle hook 32 which isarranged behind the needle plate 30 and contains the under-threadsupply. The needle 29 is curved about the axis of the shaft 28.

During the penetration of the needle 29, the edge strip 16 is clampedfirmly between the needle plate 30 and the presser 31. When the needleis pulled out of the edge strip 16, the needle plate 30 and the presser31 move apart in order to release the edge strip. The opening andclosing movement of the presser 31 is controlled by the needle lever 27which, when the needle is pulled out of the material, engages a stop 33of the presser 31 so that the presser is lifted from the edge strip 16against the action of the spring 34 which pulls said presser in thedirection of the needle plate 30.

The needle plate 30 is also removed from the edge strip when the needleis withdrawn. This is effected by the fact that an arm 35 carrying theneedle plate 30 is moved by a cam control 36 synchronized with theneedle lever movement.

On the needle plate 30 or on the presser 31, a sensor 37 is providedwhich detects the presence of the edge strip 16 and makes the sewingmachine inoperative when an edge strip has not been detected. Thissensor can be a light-cell barrier, for example, in which the lightemitter is fitted on the needle plate 30 and the receiver on the presser31.

According to FIG. 4, the thread 38 coming from a yarn bobbin (notillustrated) passes over a roller 39 driven by a stepping motor andfurther over a diverting pin 40 to the thread take-up 41 movable up anddown in the rhythm of the needle movement. From there, the thread 38passes to a thread brake 42 provided on the needle lever 27 and furtherto the needle hole arranged close to the tip of the needle 29. Thestepping motor driving the roller 39 is set into function in every cycleafter completion of the upward movement of the thread take-up 41 inorder to provide for the amount of thread which corresponds to thepredetermined stitch length. A pressing roller presses the thread firmlyagainst the roller 39 driven by the stepping motor such that the threadis moved by the roller 39 without slippage. When the roller 39 stopsmoving, it is held by the stepping motor so that no pulling of thethread from the thread supply by the pulling forces behind the roller 39is possible.

It is assumed that the carriage 22 is in its forward end position in themovement direction of the manipulator arm 19. In this position, thelocation of penetration of the needle 29 into the material representsthe tool center point of the manipulator. The manipulator arm 19 ismoved by the manipulator 20 such that the tool center point moves alongthe intended seam line.

The drive motor 23 of the sewing machine 18 is controlled in dependenceon the movement of the manipulator arm such that the stitch length (theway from penetration point to penetration point) remains constant,independently of the feeding speed. To this end, the speed componentderived from the path encoders of the manipulator in seam direction iscompared with the speed of the sewing machine motor. Before the tip ofthe needle 29 penetrates the edge strip 16, the needle plate 30 and thepresser 31 are moved towards each other. Simultaneously, the carriage 22is moved along the guide 21 opposite the feeding movement carried out bythe manipulator arm 19 (along the intended seam line), and at a speedwhich corresponds to the feeding speed. Thereby, the sewing machine 18stops relative to the holding device 10 or the workpiece during thepenetration of the needle 29 into the material, whereas the manipulatorarm 19 is continuously moved further. The requirement for this is thatthe manipulator arm 19 is aligned parallel to the intended seamdirection. When the needle 29 has been withdrawn from the material, thecarriage 22 is moved along the guide 21 into its front end positionagain, whereas the manipulator arm 19 continues its continuous feedingmovement.

These movement conditions are shown in FIG. 5. Here, in the upperillustration, the course in time of the stitch movements s of the needle29 is shown, the amplitude increasing the farther the needle tip ispushed forward from its withdrawal position through the needle plate 30.In the lower illustration, the absolute speed v of the sewing machine 18is shown, v_(R) being the constant feeding speed of the manipulator arm19. As long as no stitch movements are performed, the sewing machine 18is in its front end position with respect to the manipulator arm 19 andit moves at the feeding speed v_(R). When a stitch movement is made, thesewing machine 18 moves along the guide 21 opposite to the direction ofthe feeding speed so that the absolute speed becomes zero. Afterwithdrawal of the needle tip from the material, the sewing machine 18 ismoved along the guide 21 into the front end position again, this feedingmovement overlaying with the feeding speed v_(R) of the manipulator arm19. In the front end position, the carriage 22 remains until the nextstitch is carried out. The drive of the carriage 22 with respect to theguide 21 is effected by the sewing machine drive and in synchronizationwith the needle movements.

In the embodiment of FIG. 6, the sewing machine 48 is firmly and rigidlyconnected with the manipulator arm (not illustrated), and the componentsof the sewing head 26 are displaceable opposite to the direction of theintended sewing direction indicated by the arrow 49. The components ofthe sewing machine 48, insofar as they correspond to the components ofthe above-described sewing machine 18, are provided with the samereference numbers. The following description is restricted to thedifferences of the sewing machine 48 compared with the sewing machine18.

On the sewing machine 48, the needle lever 27 is not rigidly connectedwith the shaft 28, but is displaceable along this shaft. In the sameway, the arm carrying the presser 31 is secured to the shaft 28 forrotation therewith, but is displaceable along this shaft.

Displacement of the needle lever 27 and the presser 31 is effected by afork 50 controlled by a cam disk, said fork engaging in an annulargroove in a sleeve 51 located on the shaft 28 and being controlledsynchronously with the needle drive. In a similar manner, the needleplate 30 and the shuttle hook 32 are displaceable in the direction ofthe arrow 49 and in the opposite direction.

The seam 17 is sewn on the workpiece such that the double-layered edgestrip 16 outwardly protrudes from the cuttings. Subsequent to thecompletion of the seam, the workpiece is turned, the surfaces lying onthe outside during production coming to lie on the inside.

Although a preferred embodiment of the invention has been specificallyillustrated and described herein, it is to be understood that minorvariations may be made in the apparatus without departing from thespirit and scope of the invention, as defined the appended claims.

I claim:
 1. A device for making seams on objects comprising a holdingdevice (10) for holding material (12, 14) to be sewn together, and amanipulator (20) carrying a sewing machine (18) which causes relativemovement between the sewing machine (18) and said holding device (10)along an intended seam line by means of a manipulator arm (19) of saidmanipulator (20), characterized in that said sewing machine (18)includes a sewing head (26) with a needle plate (30) defining anabutment for the material (12, 14), a presser (31) of said sewingmachine (18) for pressing the material (12, 14) against said needleplate(30), a needle (29) of said sewing machine head (26) being movabletransversely with respect to the material (12, 14), and means forcontrolling the operation of said sewing head (26) such that said sewinghead (26) is at a standstill relative to said holding device (10) duringthe penetration of said needle (29) into the material (12, 14).
 2. Thedevice according to claim 1 including means for controlling theoperation of said manipulator arm (19) such that said sewing head (26)continuously moves at a feeding speed along the intended seam line, andmeans for driving said sewing head (26) relative to said manipulator arm(19) parallel to a feeding direction of said sewing head (26) such thatsaid sewing head (26) is moved opposite to the feeding direction of saidmanipulator arm (19) during the penetrations and in the feedingdirection of said manipulator arm (19) between penetrations.
 3. Thedevice according to claim 2, characterized in that said sewing head (26)is arranged on said sewing machine (18) in a fixed position, and saidentire sewing machine (18) on the manipulator arm (19) is movableparallel to the feeding direction.
 4. The device according to claim 2,including means for moving said sewing machine (18) relative to saidmanipulator arm (19) parallel to the feeding direction.
 5. The deviceaccording to claim 1, including means for moving apart said needle plate(30) and said presser (31) when said needle (29) is moved out of thematerial, and are moved towards each other for clamping the materialbefore said needle penetrates the material again.
 6. The deviceaccording to claim 1, characterized in that at least one sensor (37) fordetecting the presence of material between said presser (31) and saidneedle plate (30) is provided on said sewing head (26).
 7. The deviceaccording to claim 1, characterized in that said needle (29) is arrangedon a needle arm (27) connected with a shaft (28) for rotation therewithand is curved relative to said shaft (28).
 8. The device according toclaim 1, characterized in that said drive motor (23) of said sewingmachine (18) is controlled in dependence on the movement of saidmanipulator arm (19) such that the stitch length remains constantindependently of the feeding speed.
 9. The device according to claim 1,characterized in that said sewing machine comprises a thread feed with astepping motor which, for each cycle of the needle movement, provides athread amount which corresponds to a set stitch length.